Engine systems may utilize recirculation of exhaust gas from an engine exhaust system to an engine intake system, a process referred to as exhaust gas recirculation (EGR), to reduce regulated emissions. For example, a turbocharged engine system may include a low-pressure (LP) EGR system which recirculates exhaust gas from the exhaust system to the intake passage upstream of a turbocharger compressor. An intake oxygen sensor (IAO2) may be located in the engine intake downstream from the compressor and a charge air cooler to provide an indication of EGR flow based on a measured water content of the intake air.
The inventors herein have recognized various issues with the above system. In particular, intake oxygen sensor (IAO2) measurements for determining exhaust gas recirculation (EGR) in low pressure EGR vehicle systems may give an inaccurate indication of the EGR flow if water from another source contacts the IAO2. For example, when the IAO2 is positioned downstream of the charge air cooler (CAC), condensate formed at the CAC may exit the CAC and splash against the IAO2. As a result, the IAO2 may measure a higher water concentration than what may actually be attributed to the water vapor content of the EGR in the intake air. A higher EGR flow rate may then be indicated based on the output of the IAO2 sensor than the actual EGR flow rate. In some examples, using this inaccurate EGR measurement may trigger diagnostic routines, as well as inaccurately adjusting spark timing or other combustion parameters.
In one example, the issues described above may be addressed by a method for indicating water at an oxygen sensor positioned in an engine intake based on a transient increase in power consumed by a heating element of the oxygen sensor. Specifically, the oxygen sensor may be positioned downstream of a charge air cooler (CAC). When water contacts the oxygen sensor, the power consumption of the heating element may increase. Indicating water at the oxygen sensor may include indicating an amount of water at the oxygen sensor based on an amount of the transient increase in power consumed by the heating element. For example, as the power consumption of the heating element increases farther above a baseline power consumption level, the amount of water indicated at the oxygen sensor may increase. In response to an indication of water at the oxygen sensor, one or more of spark timing and a position of an intake throttle may be adjusted. Additionally, in response to the indication of water at the oxygen sensor, EGR diagnostics and/or oxygen sensor heating element diagnostics may be disabled. In one example, disabling EGR diagnostics may include disabling engine operating parameter adjustments based on EGR flow estimates, the EGR flow estimates based on oxygen sensor output. In this way, when water is indicated at the oxygen sensor, EGR flow estimates may not be used to adjust spark timing or other combustion parameters, or trigger diagnostic routines. As a result, combustion stability and accuracy of engine control may be increased. Further, adjusting the intake throttle and/or spark timing while water is indicated at the oxygen sensor may reduce combustion instability due to the ingestion of water at the engine.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.